1. Field of the Invention
The present invention relates to a preparation process of fluorine substituted aromatic compounds, and more specifically, relates to a process for preparing substituted fluorobenzene, fluorine substituted benzophenone and fluorine substituted diaryl sulfone by fluorinating an alkali metal or alkali earth metal salt of corresponding hydroxy aromatic compounds.
2. Prior Art of the Invention
Fluorine substituted aromatic compounds have specific characteristics due to fluorine and some compounds are useful in industry.
For example, substituted fluorobenzene is applied to a raw material or intermediate of physiologically active substances or functional materials for use in medicines and agriculture chemicals, and is also utilized in a wide field such as refrigerant, resin material and lubricant. Fluorine substituted benzophenone is also generally used for a raw material of polyether polyketone including polyether ether ketone which is a superengineering plastic having excellent thermal resistance, electrical insulation, sliding property and chemical resistance.
Fluorine substituted benzophenone is also used for flame retardant, painkiller, platelet aggregation inhibitor, thrombosis inhibitor and other functional chemicals or an intermediate of these functional chemicals and thus is also useful in the field of medicines and agricultural chemicals.
Further, fluorine substituted diaryl sulfone is commonly used for a raw material of polysulfone including polyether sulfone which is an engineering plastic having excellent thermal resistance, electrical insulation, sliding property and chemical resistance, and is also used for a raw material of functional materials such as an organic EL material and an intermediate of medicines and agricultural chemicals such as an anti-cancer drug and immune deficiency suppressor and thus is a required compound in industry.
The preparation process of these compounds has conventionally been investigated and following processes have been known.
The preparation process of substituted fluorobenzene can be divided into two main classes, that is, a process for preparing the desired compound by carrying out the reaction using fluorobenzene which already contains a fluorine atom, and a process for preparing the desired compound by the fluorine substituting reaction of benzene compounds having various functional groups.
The former process often uses expensive raw materials. On the other hand, the latter process can prepare the desired, substituted fluorobenzene by using cheap raw materials and thus fluorinating reaction technology which enables the desired substituted reaction has been demanded.
The following processes have been known for preparing fluorine substituted benzophenone.
EP 69598, EP 178184, EP 147299 and Japan Laid Open SHO 61-221146 have disclosed a Friedel-Crafts reaction using fluorobenzene and p-fluoro-benzoyl chloride.
Japanese Laid Open Patent SHO 58-126829 has disclosed a preparation process from 1,1-bis(4-fluorophenyl)-2,2-dichloroethylene, Japanese Laid-Open Patent SHO 57-154139 has disclosed a process from 1,1-bis(4-fluorophenyl)-2,2-trichloroethanol, and AU 533574 and Japanese Laid Open Patent SHO 57-169441 have disclosed a process from 4,4'-dichlorobenzophenone.
These preparation processes use raw materials containing fluorine or other halogen atoms, and thus much labor is required in the raw material preparation step.
As to a process for substituting fluorine for a functional group on an aromatic ring, the Balz-Schiemann reaction which replaces an amino group has been known and also utilized for preparing fluorine substituted benzophenone as desired in Japanese Laid-Open Patent SHO 54-132558. In the process, a large excess of hydrogen fluoride has been used for replacing the amino group with fluorine.
Further, conventionally known processes for preparing fluorine substituted diaryl sulfone from fluorobenzene and other fluoro aromatic compounds as a starting material are a process for reacting with chloro-sulfonic acid or fluoro-sulfonic acid as described in J. Am Chem. Soc., 62, 5111940, Japanese Laid Open Patent SHO 58-206552 and HEI 1-250342; a process for reacting with concentrated sulfuric acid in the presence of boron trifluoride and hydrogen fluoride as described in EP 147298; and a process for reacting with aryl-sulfonyl chloride as described in J. Am. Chem. Soc., 70, 654(1948) and J, Japan Chem. Soc., 76, 775-8(1955).
Other processes by using oxidation reaction of 4,4'-difluorodiphenyl sulfide and 4,4'-difluorodiphenyl sulfoxide have been described in J. Am. Chem. Soc., 70, 1564 (1948) and Acta, Chim. hug., 4, 111(1954). Any of these processes uses expensive fluoro-aromatic compounds as a raw material and is thus disadvantageous in industry.
On the other hand, fluorinating agents which have been used for a fluorination reaction include fluorine, hydrogen fluoride, sulfur tetra-fluoride and diethylaminosulfur trifluoride.
However, these conventional fluorinating agents are difficult to handle because of toxicity, corrosive property, and danger of explosion during the reaction time and thus specific equipment and technique have been required. For example, representative fluorinating agents which are effective for a direct conversion reaction from a hydroxyl group to a fluorine group include sulfur tetrafluoride (SF.sub.4) and diethylaminosulfur trifluoride (DAST).
However, SF.sub.4 has high toxicity and difficulty in handling causes problems.
On the other hand, DAST has been known as an useful fluorinating agent which can efficiently fluorinate a hydroxyl, ketone, carboxyl and other oxygen containing groups under mild conditions as described in U.S. Pat. No. 3,976,691. However, DAST is prepared by reacting highly dangerous SF.sub.4 with dimethylaminotrimethyl silane at a low temperature from -78.degree. C. to -60.degree. C, and thus specific reaction equipment is required.
As to safety, explosion in the preparation and use of DAST has been reported in J. Fluorine Chem., 42, 137 (1989).
As mentioned above, fluorine gas, hydrogen fluoride and sulfur tetrafluorine gas have been conventionally used as a fluorinating agent for preparing a fluorine compound.
These fluorinating agents have led to problems upon difficulty in handling due to toxicity, corrosive property, danger of explosion during the reaction time, and requirement for specific equipment and technique. In recent years, various fluorinating agents have been developed in order to overcome these problems.
However, the development of a fluorinating agent, which can be used in industry, has been still unsatisfactory in view of a preparation process, selectivity in the reaction, yield and economy.
Thus, a safe, steady and economical preparation process of fluorine substituted benzophenone by using a fluorinating agent has not yet been found.
Another process for reacting diaryl-sulfone which has halogen other than fluorine or a nitro group as a substituent with KF at a high temperature above 200.degree. C. in an aprotic polar solvent in the presence of a specific ammonium salt or an organometal complex has been described in WO 8704148-8704150 and Japanese Laid Open Patent HEI 2-273626.
However, these processes are difficult in reaction conditions and thus unfavorable in industry. A process for reacting 4,4'-dinitrodiphenyl sulfone with tetramethylammonium fluoride under relatively mild condition in an aprotic polar solvent has been reported in J. Fluorine Chem., 70(2), 201(1995). However, pure tetramethylammonium fluoride is difficult to prepare and thus is an expensive fluorinating agent. Consequently, the process is also disadvantageous in industry.
Under these circumstances, it has been strongly desired for fluorine substituted diaryl sulfone to develop an economical and readily realizable preparation process in industry.